1. Field of the Invention
The present invention relates to a solenoid-operated valve control apparatus for an internal combustion engine, and in particular to such a solenoid-operated valve control apparatus that is adapted to open and close a valve body that functions as an intake or exhaust valve of the engine, using spring force and electromagnetic force, and a solenoid-operated valve control method.
2. Description of the Related Art
An example of a known solenoid-operated valve control apparatuses for an internal combustion engine is disclosed in Japanese Patent Laid-Open Publication No. HEI 9-250318. In the solenoid-operated valve control apparatus of the engine, each solenoid-operated valve includes a valve body that functions as an intake or exhaust valve of the engine, a pair of springs that biases the valve body in a valve opening direction and in a valve closing direction, and a pair of electromagnetic coils that generate electromagnetic forces that move the valve body in the valve opening direction and the valve closing direction. With this arrangement, the known solenoid-operated valve described above is able to drive the valve body to open and close the same by alternately energizing each of the electromagnetic coils at an appropriate timing.
When the engine is operated for a long period of time, carbon produced by oxidation or deterioration of engine oil or fuel, for example, may be deposited between the intake or exhaust valve and a valve seat against which the intake/exhaust valve is seated. If carbon is deposited in such a manner, the valve body is not appropriately seated on the valve seat upon closing of the valve body, and sealing between the valve body and the valve seat may deteriorate when the valve body is placed in the closed position.
In this apparatus, an exciting current supplied to the upper coil while the valve is held in the closed position is increased to a value larger than that during normal operations. In this method, an electromagnetic force applied in the valve closing direction is increased while the valve body is held in the closed position so that the above-described carbon deposits can be crushed between the valve body and the valve seat. With the apparatus of the related art, therefore, it is possible to prevent a reduction in the sealing between the valve body and the valve seat due to the presence of carbon when the valve body is in the closed position.
In the above-described apparatus, the electromagnetic force applied in the valve closing direction increases after the valve body has reached its closed position. Therefore, carbon deposited between the valve body and the valve seat will always be crushed by the same portion of the valve body. This may result in increased wear of a local area of the abutting face of the valve body on the valve seat.